This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Enterohemorrhagic E. coli (EHEC) O157:H7 contributes greatly to the enormous economic and health burden of food borne disease. The mechanisms by which EHEC Type III Secretion System (T3S) effector proteins modulate host signaling pathways are incompletely characterized. This project will be significant because it will define the mechanism by which the EHEC effector proteins NleH1 and NleH2 disrupt the normal host innate immune response to bacterial infection. The central hypothesis for the proposed research is that NleH proteins bind to the NF-kB subunit RPS3 to disrupt specific host transcriptional responses to bacterial infection. We will test our central hypothesis and accomplish the overall objective of this application by pursuing the following specific aims: Aim 1. Map the NleH-Rps3 binding domains. Our working hypothesis is that NleH1 and NleH2 bind the mammalian non-Rel NF-kB subunit RPS3 to subvert its normal function. Aim 2. Quantify the influence of NleH1/NleH2 translocation on host transcription. Our working hypothesis is that NleH1 represses NF-kB-dependent host transcription, whereas NleH2 stimulates NF-kB. Aim 3. Measure the contribution of NleH1/NleH2 to bacterial virulence in animal models of attaching/effacing pathogens. Our working hypothesis is that NleH1/NleH2 promote bacterial transmission by maintaining an optimal balance between bacterial colonization vs. host inflammatory responses. The proposed research is innovative because it will test the hypothesis that translocated bacterial protein kinases subvert the host innate response to infection by disrupting a novel molecular specifier of selected host transcriptional responses to external stimuli.